: The investigators propose to develop a high resolution genetic map of chromosome 1. This chromosome is approximately 350 cM long and contains approximately 10% of the entire genome. First, an "index map" of chromosome 1 with approximately 35 highly informative markers (H greater than or equal to 0.70) spaced at 10 cM intervals along the chromosome will be constructed by the addition of approximately 25 markers to the highly informative markers in the current map. Second, a high resolution (1-2 cM) genetic map containing approximately 200 loci spaced at 1-2 cM intervals will be developed by the addition of 100 markers to the 101 loci in the current chromosome 1 genetic map. The maps will be built by the addition of many highly informative (CA)n microsatellite polymorphisms to the current map which is primarily built with less informative restriction fragment length polymorphisms (RFLPs). The index map of 35 highly informative markers will be completed within 2 years and the 1-2 cM high resolution map will be completed within 5 years.